Bind ListBox with DataTable

Hello everybody,

I have a method in my business class and I send reference of a listbox to that method to fill it. Method first fills fetches the records in a DataTable and then binds the DataTable with ListBox. Here is the code.

Code:

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public void Fill(ref System.Web.UI.WebControls.ListBox thisList)
{
    //  Object of Data Access Layer - Related Class
    DataAccessLayer.Group groupDAL = new DataAccessLayer.Group();
    groupDAL.GetAll();
                                       
    int count = 0 ;
    DataTable dtTemporary  = new DataTable();
    dtTemporary.Clear();
    DataColumn dc1 = new DataColumn("ID",Type.GetType("System.Int32"));
    DataColumn dc2 = new DataColumn("Name",Type.GetType("System.String") );
    dtTemporary.Columns.Add(dc1);
    dtTemporary.Columns.Add(dc2);
    while ( groupDAL.Read() )
    {
        count++;
        DataRow rowgroup = dtTemporary.NewRow();
        rowgroup["ID"] =  groupDAL.ID;
        rowgroup["Name"] =  groupDAL.Name;
        dtTemporary.Rows.Add(rowgroup);
      }
    groupDAL.Dispose();
    thisList.DataSource = dtTemporary;
    thisList.DataTextField = "Name";
    thisList.DataValueField = "ID";                                       
}

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I am getting the error messages, "Object reference not set to an instance of an object" on this line.

thisList.DataSource = dtTemporary;

Thanks.